This invention relates to the conversion of coal and similar carbonaceous solids into liquids and is particularly concerned with a staged temperature coal conversion process.
Among the more promising processes for the production of liquid hydrocarbons from coal are those in which the feed coal is first contacted with molecular hydrogen and a hydrogen-donor solvent in a liquefaction zone at elevated temperature and pressure to break down the complex high molecular weight constituent of the feed material into lower molecular weight hydrocarbon liquids and gases. A portion of the liquids produced in the liquefaction reactor are recovered and catalytically hydrogenated in a solvent hydrogenation reactor to generate the hydrogen-donor solvent required in the liquefaction step. The heavy liquefaction product, which normally boils in excess of 1000.degree. F., recovered from the liquefaction reactor may be upgraded by subjecting it to pyrolysis to produce gases, additional hydrocarbon liquids, and coke which is subsequently steam gasified to form hydrogen and carbon monoxide for use as fuel.
Although the process outlined above has numerous advantages over other liquefaction processes and produces a relatively large amount of liquids, it does require the use of a hydrogen-donor solvent produced by hydrogenating a portion of the liquid product in an external catalytic hydrogenation reactor. The production of this hydrogen-donor recycle solvent stream via catalytic hydrogenation external to the liquefaction step adds appreciably to the cost of the process and it would therefore be economically attractive if the recycle stream could be eliminated without decreasing the liquid yield from the process.